Distributed propulsion system for vertical take off and landing closed wing aircraft

ABSTRACT

An aircraft includes a closed wing, a fuselage at least partially disposed within a perimeter of the closed wing, and one or more spokes coupling the closed wing to the fuselage. A plurality of hydraulic or electric motors are disposed within or attached to the closed wing, fuselage or spokes in a distributed configuration. A propeller is proximate to a leading edge of the closed wing or spokes and operably connected to each hydraulic or electric motor. A source of hydraulic or electric power is disposed within or attached to the closed wing, fuselage or spokes and coupled to each hydraulic or electric motor disposed within or attached to the closed wing, fuselage or spokes. A controller is coupled to each hydraulic or electric motor, and one or more processors communicably coupled to each controller that control an operation and speed of the plurality of hydraulic or electric motors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/336,290, filed May 13, 2016 entitled “Distributed Propulsion”,U.S. Provisional Application Ser. No. 62/336,432, filed May 13, 2016entitled “Forward Folding Rotor Blades”, U.S. Provisional ApplicationSer. No. 62/336,363, filed May 13, 2016 entitled “Vertical Take Off andLanding Closed Wing Aircraft”, U.S. Provisional Application Ser. No.62/336,420, filed May 13, 2016 entitled “Distributed Propulsion Systemfor Vertical Take Off and Landing Closed Wing Aircraft”, and U.S.Provisional Application Ser. No. 62/336,465, filed May 13, 2016 entitled“Modular Fuselage Sections for Vertical Take Off and Landing DistributedAirframe Aircraft”, the entire contents of which are incorporated hereinby reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of aircraftdesign, and more particularly, to distributed propulsion systems forvertical take off and landing closed wing aircraft.

STATEMENT OF FEDERALLY FUNDED RESEARCH

None.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is describedin connection with aircraft. Based on a classical helicopterconfiguration improvements in helicopter productivity have been, atbest, only incremental. A classical helicopter configuration includescertain fundamental limitations that hamper improvements, e.g.,retreating blade stall, blade loading, advancing blade tip Mach number,and the large increases in power that are required with increased speed.These physical limitations contribute to increased vibration resultingpoor ride quality and reduced component life. In addition, certainphysical limitations lead to increased size and weight.

The classical approach to this problem is to develop helicopters inwhich these configuration limitations are addressed via ancillarydevices, such as wings, additional engines, and propellers.Incorporation of these approaches, due to their increased complexity andweight, reduces the economic load carrying capability of the helicopterand raises questions as to the safety of operation of the helicopter andits long term reliability.

Although the development of compound helicopters with wings, additionalengines, and propellers represents significant improvements inhelicopter productivity, considerable shortcomings remain.

SUMMARY OF THE INVENTION

An aircraft capable of vertical takeoff and landing and stationaryflight includes a closed wing, a fuselage at least partially disposedwithin a perimeter of the closed wing, and one or more spokes couplingthe closed wing to the fuselage. A plurality of hydraulic or electricmotors are disposed within or attached to the closed wing, fuselage orspokes in a distributed configuration. A propeller is proximate to aleading edge of the closed wing or the one or more spokes, operablyconnected to each of the hydraulic or electric motors and provides liftwhenever the aircraft is in vertical takeoff and landing and stationaryflight. A source of hydraulic or electric power is disposed within orattached to the closed wing, fuselage or spokes and coupled to each ofthe of hydraulic or electric motors disposed within or attached to theclosed wing, fuselage or spokes, wherein the source of hydraulic orelectric power provides sufficient energy density for the aircraft toattain and maintain operations of the aircraft. A controller is coupledto each of the hydraulic or electric motors, and one or more processorscommunicably coupled to each controller that control an operation andspeed of the plurality of hydraulic or electric motors.

A method for distributed propulsion of aircraft capable of verticaltakeoff and landing and stationary flight includes the steps ofdetermining at least one of aerodynamics, propulsive efficiency,structural efficiency, and weight of the aircraft, selecting a number,size and type of hydraulic or electric motors necessary to providedistributed propulsion for powered operations of the aircraft, selectinga power source having sufficient energy density to power the hydraulicor electric motors connected to propellers to operate the aircraft, andproviding a distributed propulsion system. The distributed propulsionsystem includes a closed wing, a fuselage at least partially disposedwithin a perimeter of the closed wing, and one or more spokes couplingthe closed wing to the fuselage. A plurality of hydraulic or electricmotors are disposed within or attached to the closed wing, fuselage orspokes in a distributed configuration. A propeller is proximate to aleading edge of the closed wing or the one or more spokes, operablyconnected to each of the hydraulic or electric motors and provides liftwhenever the aircraft is in vertical takeoff and landing and stationaryflight. A source of hydraulic or electric power is disposed within orattached to the closed wing, fuselage or spokes and coupled to each ofthe of hydraulic or electric motors disposed within or attached to theclosed wing, fuselage or spokes, wherein the source of hydraulic orelectric power provides sufficient energy density for the aircraft toattain and maintain operations of the aircraft. A controller coupled toeach of the hydraulic or electric motors, and one or more processorscommunicably coupled to each controller that control an operation andspeed of the plurality of hydraulic or electric motors.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the present applicationare set forth in the appended claims. However, the system itself, aswell as a preferred mode of use, and further objectives and advantagesthereof, will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear, wherein:

FIG. 1A is a perspective view of a closed wing aircraft in accordancewith one embodiment of the present invention;

FIG. 1B is a front elevation view of the closed wing aircraft of FIG.1A;

FIG. 1C is a rear elevation view of the closed wing aircraft of FIG. 1A;

FIG. 1D is a right side elevation view of the closed wing aircraft ofFIG. 1A;

FIG. 1E is a left side elevation view of the closed wing aircraft ofFIG. 1A;

FIG. 1F is a top plan view of the closed wing aircraft of FIG. 1A;

FIG. 1G is a bottom plan view of the closed wing aircraft of FIG. 1A;

FIG. 2 shows a schematic of a hybrid turboshaft engine hydraulicdistributed propulsion system in accordance with one embodiment of thepresent invention;

FIG. 3 shows a schematic of a hybrid internal combustion engine—enginehydraulic distributed propulsion system in accordance with oneembodiment of the present invention;

FIG. 4 shows a schematic of a hybrid electric hydraulic distributedpropulsion system in accordance with one embodiment of the presentinvention;

FIG. 5 shows a schematic of a hybrid electric hydraulic with apiezo-electric pump distributed propulsion system in accordance with oneembodiment of the present invention;

FIG. 6A depicts the closed wing aircraft of FIG. 1A in stationary flight(hover mode including vertical take off and landing) in accordance withone embodiment of the present invention;

FIG. 6B depicts the closed wing aircraft of FIG. 1A in transition fromstationary flight to forward flight and vice versa in accordance withone embodiment of the present invention;

FIG. 6C depicts the closed wing aircraft of FIG. 1A in forward flight inaccordance with one embodiment of the present invention

FIG. 7A is a perspective view of a closed wing aircraft in accordancewith one embodiment of the present invention in which the rotors on thespokes are deployed and the rotors on the closed wing are foldedforward;

FIG. 7B is a front elevation view of the closed wing aircraft of FIG.7A;

FIG. 7C is a rear elevation view of the closed wing aircraft of FIG. 7A;

FIG. 7D is a right side elevation view of the closed wing aircraft ofFIG. 7A;

FIG. 7E is a left side elevation view of the closed wing aircraft ofFIG. 7A;

FIG. 7F is a top plan view of the closed wing aircraft of FIG. 7A;

FIG. 7G is a bottom plan view of the closed wing aircraft of FIG. 7A;

FIG. 8 is a perspective view of a closed wing aircraft in accordancewith one embodiment of the present invention in which the rotors on thespokes are deployed and the rotors on the closed wing are foldedbackward;

FIG. 9A is a perspective view of a closed wing aircraft having asinusoidal-shaped circular wing in accordance with one embodiment of thepresent invention;

FIG. 9B is a front elevation view of the closed wing aircraft of FIG.9A;

FIG. 9C is a rear elevation view of the closed wing aircraft of FIG. 9A;

FIG. 9D is a right side elevation view of the closed wing aircraft ofFIG. 9A;

FIG. 9E is a left side elevation view of the closed wing aircraft ofFIG. 9A;

FIG. 9F is a top plan view of the closed wing aircraft of FIG. 9A; and

FIG. 9G is a bottom plan view of the closed wing aircraft of FIG. 9A.

DETAILED DESCRIPTION OF THE INVENTION

While the system of the present application is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the present application tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present application as defined by theappended claims.

To facilitate the understanding of this invention, a number of terms aredefined below. Terms defined herein have meanings as commonly understoodby a person of ordinary skill in the areas relevant to the presentinvention. Terms such as “a”, “an” and “the” are not intended to referto only a singular entity, but include the general class of which aspecific example may be used for illustration. The terminology herein isused to describe specific embodiments of the invention, but their usagedoes not delimit the invention, except as outlined in the claims.

Illustrative embodiments of the present application are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

As used herein, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

In aerospace technology, distributed propulsion is defined asdistributing the airflows and forces generated by the propulsion systemabout an aircraft in a way that improves the vehicle's aerodynamics,propulsive efficiency, structural efficiency, and aeroelasticity. Whiledesigns have been proposed in which airplanes include a series of smallengines or motors along the surfaces and on vertical lift platforms bythe assembly of a matrix of small engines or motors. However, thecomplexity and weight of installing large numbers of conventionalturbine or internal combustion engines to achieve distributed propulsionis impractical for all but very large aircraft. For example,mechanically interconnecting multiple propellers using gearboxes andshafts to achieve distributed propulsion can reduce weight, but itsacrifices the ability to independently control propellers or fans toprovide thrust vectoring for control and aerodynamic efficiency.

While many applications of electric motors to achieve practicaldistributed propulsion has attracted major interest by NASA, DARPA, andthe aerospace industry, the power density necessary to attain andmaintain flight using electric motors and batteries has simply not beenfeasible. While higher energy density batteries are in development, pureelectric propulsion in combination with distributed propulsion, whileattractive, has not been attained for anything except small drones andtoys.

For example, current Li-ion battery technology is capable of achievingan energy density that would require an impractically heavy Li-ionbattery. Thus, using current battery technology, electric distributedpropulsion development requires the application of electric generatorsdriven by turbo shaft engines. Replacing battery technology withgenerators driven by turbo shaft engines reduces system weight onlymarginally.

With the adoption of generators driven by turbo shaft engines in placeof battery technology, the remaining major obstacle to achievingpractical electric distributed propulsion is electric motor andassociated controller technology. However, current electric motortechnology and performance falls short of meeting the requirements forsupporting practical application of distributed electric propulsion. Aselectric motor power and torque output is increased beyond therequirements of small drones to levels suitable for larger aircraft, theissues of power density (Watts of shaft power generated per kilogram ofweight), cooling and lubrication lead to impractical increases inweight. Further, even when analyzing the performance of the mostadvanced electric motors the additional weight for cooling systems,lubrication systems, or required electric power controllers thatregulate motor speed and torque are impractical or lead to nosignificant improvements in overall aircraft performance.

The present invention can use variable displacement hydraulic motors,with the advantage that speed and torque are controlled by changing thedisplacement of the motor. This is equivalent to having a variable speedtransmission in a gearbox or being able to instantly change the size ofan electric motor to suit required power demands. Changing the motordisplacement requires very little power and can be achieved using servovalve adding very little weight. This added weight to control thehydraulic motor is independent of the rated power on the motor. When theadded weight for the hydraulic motor controllers is added to the motorweight a significant improvement was obtained. Further, no additionalweight for hydraulic motor lubrication or motor and controller coolingis required for hydraulic motors, as these are already part of the motorweight.

Further, when one compares the weight and volume of hydraulic tubingversus electrical cable required for transmission of power at themagnitudes required for larger aircraft, a benefit is also obtained, or,the values are basically equivalent. Thus, the hydraulic distributedpropulsion system of the present invention is lighter than the mostefficient, equivalent electric system.

Thus, the present invention takes advantage of the best cost-to-benefitratio for use of hydraulic and electric motor propulsion. For example,the present invention uses the best of the possible high power systemsperformance aspects, including but not limited to, weight motor andcontroller, envelope for motor and controller installation, supplementalmotor cooling required, supplemental motor lubrication required, highmotor torque and low rotational inertia, motor reliability (notincluding controller), weight for transmission of power, and totalsystem efficiency using engine.

The invention addresses the limitations of electric motor, generator andbattery technology as applied to the field of distributed propulsion foraircraft. By using variable displacement hydraulic pump and motortechnology, distributed propulsion for larger aircraft is practical. Invariable displacement hydraulic motors, speed and torque is controlledby changing the displacement of the motor. This is equivalent to havinga variable speed transmission in a gearbox or being able to instantlychange the size of an electric motor to suit required power demands.Compared with controlling electric motor speed using Pulse WidthModulation, changing hydraulic motor displacement requires very littlepower and negligible weight.

As will be described in more detail below, various embodiments of thepresent invention integrate a circular wing or ring wing configurationwith a distributed a propulsion system to create a vertical takeoff andlanding (VTOL) aircraft configuration with long range and high speed.These performance capabilities are achieved without increased aircraftcomplexity and cost normally incurred with this level of capability in aVTOL aircraft. No reconfiguration of the aircraft is required totransition between vertical hover and horizontal airplane mode flight.The “tail sitter” or “pogo” configuration allows transition without anyphysical configurations. However, in some embodiments, structural,aerodynamic or power plant adjustments and/or reconfigurations may bedesirable. In some embodiments, the rotor blades of the closed wingmounted propellers can be folded either forward or back to furtherreduce drag and provide increased speed and duration.

Now referring to FIGS. 1A-1G, various views of a closed wing aircraft100 in accordance with one embodiment of the present invention areshown. More specifically, FIG. 1A is a perspective view, FIG. 1B is afront elevation view, FIG. 1C is a rear elevation view, FIG. 1D is rightside elevation view, FIG. 1E is a left side elevation view, FIG. 1F is atop plan view, and FIG. 1G is a bottom plan view. This closed wingaircraft 100 features the following: 1) Tail sitter configurationprovides for conversion to airplane mode without reconfiguration; 2)Circular wing optimizes propulsion, structural, aerodynamic, and centerof gravity (CG) requirements; 3) Gearboxes and drive train arecompletely eliminated; 4) Rotor cyclic and collective controls arereplaced by variable speed constant pitch propellers; and 5) Yaw invertical flight and roll in hover mode are provided by trailing edgesurfaces on the spokes connecting the closed wing to the fuselage.

The closed wing aircraft 100 utilizes the ring wing configuration toprovide a symmetric matrix distribution of hydraulic or electric motordriven propellers to maximize controllability and provide safety in theevent of a hydraulic or electric motor failure. The ring wing alsoreduces the effects of cross winds during takeoff and landing byminimizing the affected wing area and eliminating induced yaw. Inairplane mode flight the ring wing allows the aircraft maintain any rollposition in order to position sensors as required. For noise reductionthe propellers within the ring provide an acoustic barrier.Structurally, the combination of distributed propulsion and the ringwing minimizes bending moments allowing for lighter and stifferstructure compared with distributed propulsion on straight wings.Engines or fuel/batteries can be housed in the base of the fuselage orat the intersection of the spokes to the ring wing for strength andminimization of weight. Landing gear is positioned at these points forsimilar reasons.

More specifically, the aircraft 100 can be manned or unmanned and iscapable of vertical takeoff and landing, stationary flight and forwardflight. The aircraft 100 includes a closed wing 102, a fuselage 104 atleast partially disposed within a perimeter of the closed wing 102, andone or more spokes 106 coupling the closed wing 102 to the fuselage 104.The closed wing 102 can be circular-shaped, oval-shaped,triangular-shaped, polygonal-shaped or any other shape suitable for thedesired operational and aerodynamic requirements of the aircraft 100. Inaddition, the closed wing can be made up of a plurality of wing segments102 a, 102 b, 102 c and wing-spoke intersections or junctions 108 a, 108b, 108 c connected together. The cross-sectional profile of the closedwing 102 between the leading edge 110 and trailing edge 112 can be asymmetrical airfoil or any desirable aerodynamic shape. The number ofspokes 106 can be determined, in part, by the shape and size of theclosed wing 102, and the shape, size and payload of the fuselage 104.The cross-sectional profile of the spokes 106 between the leading edge114 and the trailing edge 116 can be a symmetrical airfoil or anydesirable aerodynamic shape. The closed wing 102, the fuselage 104 andthe one or more spokes 106 are preferably symmetrically shaped toprovide transition between vertical takeoff and landing, stationaryflight and forward flight in any direction. However, non-symmetricalshapes can be used. As a result, the shape of the closed wing 102 andnumber of spokes 106 shown in the figures is only one example and is notintended to limit the scope of the invention. The closed wing 102 mayalso include one or more doors or removable sections that provide accessto the fuselage 104 when the aircraft 100 is in a landed position.

The fuselage 104 may include one or more sections or modules that have alongitudinal axis 116 substantially parallel to a rotational axis 118 ofthe propellers 120. The shape and length of the fuselage 104 will varydepending on the desired mission and flight characteristics. As aresult, the shape and length of the fuselage 104 shown in the figures isonly one example and is not intended to limit the scope of theinvention. For example, the fuselage 104 may include a rear section ormodule 122 substantially disposed at a center of the closed wing 102that provides a fuselage-spoke intersection or junction, a middlesection or module 124 connected to the rear section or module 122, afront section or module 126 connected to the middle module 124, and anose section or module 128 connected to the front section or module 126.Sections or modules 122, 124, 126, 128 can be removably connected to oneanother, which makes the aircraft 100 configurable for any desiredmission or function. In other words, the closed wing 102 and one or morespokes 106 provide a stable flight platform any desired payload.Moreover, the middle 124, front 126 and nose 128 sections or modules candetach, pivot, or retract at least partially into one or more of theother sections or modules for storage or transport of the aircraft 100.The rear 122, middle 124, front 126 and nose 128 sections or modules canbe individually configured to be a cockpit module, a cabin module, anescape module, a payload module, a sensor module, a surveillance module,a power source module, a fuel module, or any combination thereof. Notethat the nose section or module 128 may contain one or more parachutes.

The aircraft 100 also includes three or more landing gear, pads or skids130 operably attached to the closed wing 102. Typically, the landinggear, pads or skids 130 will be disposed proximate to the wing-spokeintersections or junctions 108 a, 108 b, 108 c where there is morestructural support. The landing gear, pads or skids 130 can beretractable.

One or more engines or motors 132 are disposed within or attached to theclosed wing 102, fuselage 104 or spokes 106 in a distributedconfiguration. Three or more propellers 120 are proximate to the leadingedge 110 of the closed wing 102 or the leading edge 114 of the one ormore spokes 106, distributed along the closed wing 102 or the one ormore spokes 106, and operably connected to the one or more engines ormotors 132. In the embodiment shown, nine propellers 120 are disposedproximate to the closed wing 102, and one propeller 120 is disposedproximate to each spoke 106. The propellers 120 can be variable speedconstant pitch propellers or other type of propeller. The distributionand number of propellers 120 are designed to provide stability duringthe failure of one or more propellers 120, or engines or motors 132.

In one embodiment, a source of hydraulic or electric power is disposedwithin or attached to the closed wing 102, fuselage 104 or spokes 106and coupled to each of the of hydraulic or electric motors 132 disposedwithin or attached to the closed wing 102, fuselage 104 or spokes 106.The source of hydraulic or electric power provides sufficient energydensity for the aircraft to attain and maintain operations of theaircraft 100. The source of hydraulic or electric power can be one ormore batteries, a piston engine, or a turboshaft engine. A controller iscoupled to each of the hydraulic or electric motors 132, and one or moreprocessors are communicably coupled to each controller that control anoperation and speed of the plurality of hydraulic or electric motors132. Note that a single source of hydraulic or electric power can drivemultiple hydraulic or electric motors 132. For example, a source ofhydraulic or electric power can be located in the wing-spokeintersections or junctions 108 a, 108 b, 108 c or the rear fuselage 122where there is more structural support. Hydraulic or electric powerdistribution systems can be used to transmit the power to the hydraulicor electric motors 132, which in turn drive the propellers 120. Thehydraulic or electric motors 132 are selected based on at least one ofaerodynamics, propulsive efficiency, structural efficiency,aeroelasticity, or weight of the aircraft. Moreover, the propellers 120,or the engines or motors 132 can be mounted to pivot to providedirectional thrust. Similarly, additional thrusters can be disposed onthe closed wing 102, fuselage 104 or spokes 106. Various examples ofdistributed power systems are shown in FIGS. 2-5.

Referring now to FIG. 2, a schematic of a hybrid turboshaft enginehydraulic distributed propulsion system 200 in accordance with oneembodiment of the present invention is shown. In the hybrid turboshaftengine hydraulic distributed propulsion system 200, a source of fuel 202is connected to a fuel line 204 that feeds a turboshaft engine 206 thatgenerates a mechanical force that is transmitted by a mechanical shaft208 that is connected to a variable displacement hydraulic pump 210. Thevariable displacement hydraulic pump 210 is connected to, and provideshydraulic power to, hydraulic lines 212. The hydraulic fluid inhydraulic lines 212 is connected to hydraulic controllers 214 a-214 f,which are connected mechanically by mechanical shafts 215 a-215 f to thevariable displacement hydraulic motors 216 a-216 f, respectively, eachof which is depicted being connected by mechanical shafts 218 a-218 f topropellers 120 a-120 f, respectively. Changing the displacement of thevariable displacement hydraulic motors 216 a-216 f can control the speedand torque of the variable displacement hydraulic motors 216 a-216 f.The variable displacement hydraulic motors 216 a-216 f can beself-cooling. This schematic shows the Hybrid Turboshaft EngineHydraulic distributed propulsion system 200 as having six (6) hydrauliccontrollers 214 a-214 f, and six (6) variable displacement hydraulicmotors 216 a-216 f. However, the skilled artisan will recognize that thepresent invention can include a smaller or larger number of variabledisplacement hydraulic motors and propellers, for example 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 ormore. In this embodiment, the fuel is converted into mechanicalpower/energy via the turboshaft engine 206, which provides the hydraulicpower that drives the variable displacement hydraulic motors 216 a-216 fand therefore the propellers 120 a-120 f.

Now referring to FIG. 3, a schematic of a hybrid internal combustionengine—engine hydraulic distributed propulsion system 300 in accordancewith one embodiment of the present invention is shown. In thisembodiment, the hybrid internal combustion engine—engine hydraulicdistributed propulsion system 300 uses a source of fuel 202 that isconnected to fuel line 204 that feeds an internal combustion engine 302that generates a mechanical force that is transmitted by a mechanicalshaft 208 that is connected to a variable displacement hydraulic pump210. The variable displacement hydraulic pump 210 is connected to, andprovides hydraulic power to, hydraulic lines 212. The hydraulic fluid inhydraulic lines 212 is connected to hydraulic controllers 214 a-214 f,which are connected mechanically by mechanical shafts 215 a-215 f to thevariable displacement hydraulic motors 216 a-216 f, respectively, eachof which is depicted being connected by mechanical shafts 218 a-218 f topropellers 120 a-120 f, respectively. Changing the displacement of thevariable displacement hydraulic motors 216 a-216 f can control the speedand torque of the variable displacement hydraulic motors 216 a-216 f.The variable displacement hydraulic motors 216 a-216 f can beself-cooling. This schematic shows the Hybrid Internal CombustionEngine—Engine Hydraulic distributed propulsion system 300 as having six(6) hydraulic controllers 214 a-214 f, and six (6) variable displacementhydraulic motors 216 a-216 f. However, the skilled artisan willrecognize that the present invention can include a smaller or largernumber of variable displacement hydraulic motors and propellers, forexample 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25 or more. In this embodiment, the fuel is convertedinto mechanical power/energy via the internal combustion engine 302,which provides the hydraulic power that drives the variable displacementhydraulic motors 216 a-216 f and therefore the propellers 218 a-218 f.

Referring now to FIG. 4, a schematic of a hybrid electric hydraulicdistributed propulsion system 400 in accordance with one embodiment ofthe present invention is shown. In this embodiment, the hybrid electrichydraulic distributed propulsion system 400 uses one or more batteries402 that are connected to electrical cable 404 that directly powers avariable displacement hydraulic motor pump 406. The variabledisplacement hydraulic motor pump 406 is connected to, and provideshydraulic power to, hydraulic lines 212. The hydraulic fluid inhydraulic lines 212 is connected to hydraulic controllers 214 a-214 f,which are connected mechanically by mechanical shafts 215 a-215 f to thevariable displacement hydraulic motors 216 a-216 f, respectively, eachof which is depicted being connected by mechanical shafts 218 a-218 f topropellers 120 a-120 f, respectively. Changing the displacement of thevariable displacement hydraulic motors 216 a-216 f can control the speedand torque of the variable displacement hydraulic motors 216 a-216 f.The variable displacement hydraulic motors 216 a-216 f can beself-cooling. This schematic shows the Hybrid Internal CombustionEngine—Engine Hydraulic distributed propulsion system 400 as having six(6) hydraulic controllers 214 a-214 f, and six (6) variable displacementhydraulic motors 216 a-216 f. However, the skilled artisan willrecognize that the present invention can include a smaller or largernumber of variable displacement hydraulic motors and propellers, forexample 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25 or more. In this embodiment, the electrical power isconverted into mechanical power/energy via the variable displacementhydraulic motor pump 406, which provides the hydraulic power that drivesthe variable displacement hydraulic motors 216 a-216 f and therefore thepropellers 218 a-218 f.

Now referring to FIG. 5, a schematic of a hybrid electric hydraulic witha piezo-electric pump distributed propulsion system 500 in accordancewith one embodiment of the present invention is shown. In thisembodiment, the hybrid electric hydraulic with a piezo-electric pumpdistributed propulsion system 500 uses one or more batteries 402 thatare connected to electrical cable 404 that directly powers apiezo-hydraulic pump 408. The piezo-hydraulic pump 408 is connected to,and provides hydraulic power to, hydraulic lines 212. The hydraulicfluid in hydraulic lines 212 is connected to hydraulic controllers 214a-214 f, which are connected mechanically by mechanical shafts 215 a-215f to the variable displacement hydraulic motors 216 a-216 f,respectively, each of which is depicted being connected by mechanicalshafts 218 a-218 f to propellers 120 a-120 f, respectively. Changing thedisplacement of the variable displacement hydraulic motors 216 a-216 fcan control the speed and torque of the variable displacement hydraulicmotors 216 a-216 f. The variable displacement hydraulic motors 216 a-216f can be self-cooling. This schematic shows the Hybrid InternalCombustion Engine—Engine Hydraulic distributed propulsion system 500 ashaving six (6) hydraulic controllers 214 a-214 f, and six (6) variabledisplacement hydraulic motors 216 a-216 f. However, the skilled artisanwill recognize that the present invention can include a smaller orlarger number of variable displacement hydraulic motors and propellers,for example 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, 21, 22, 23, 24, 25 or more. In this embodiment, the electrical poweris converted into mechanical power/energy via the piezo-hydraulic pump408, which provides the hydraulic power that drives the variabledisplacement hydraulic motors 216 a-216 f and therefore the propellers218 a-218 f.

Some of the benefits of the distributed hydraulic system of the presentinvention, in conjunction with electric propulsion, can be attained bythe present invention, for aircraft of all sizes. For example, for usewith Vertical Take-Off and Landing (VTOL) aircraft the advantages of thepresent invention include: (1) a reduction in aircraft propulsioninstallation weight through greater structural integration; (2) theelimination of (rotor cyclic) control through differential and vectoringthrust for pitch, roll, and yaw moments; (3) high production rates andeasy replacement of motors or propulsors that are small and light; (4)in the case of turbine/IC engine electric power generation, reduced fuelconsumption and emissions through independent control of engine androtor speeds; and (5) using electric batteries provided for moreefficient energy usage, reduced emissions, and lower noise.

Further advantages of the present invention include addressing certainroad blocks to distributed electric propulsion for larger VTOL aircraft.The present invention provides one or more of the following benefits:(1) the elimination of electric motor and required controller powerdensities are low at required power levels (excessive weight); (2)eliminate electric motor torque capacity that is inadequate for speedchanges required for thrust vectoring of larger rotors; (3) withincreased power, electric motors require large diameters with ducted airor liquid cooling to prevent over heating (increasedweight/envelope/complexity); (4) with increased power electric motorbearings require active lubrication (increased weight/complexity); and(5) current battery technology energy density insufficient for practicalapplications due to excessive weight.

Referring now to FIGS. 6A-6C, the aircraft 100 is shown in stationaryflight (hover mode including vertical take off and landing) (FIG. 6A),transition from stationary flight to forward flight and vice versa (FIG.6B), and forward flight (FIG. 6C). The closed wing 102 provides liftwhenever the aircraft 100 is in forward flight. The three or morepropellers 120 provide lift whenever the aircraft 100 is in verticaltakeoff and landing and stationary flight, and provide thrust wheneverthe aircraft 100 is in forward flight. During forward flight, thepropellers 120 can be selectively feathered or operated in a low powermode because the closed wing 102 and spokes 106 provide lift. One ormore flight control surfaces are disposed on or extending from theclosed wing 102, spokes 106 or the fuselage 104 to provide improvedcontrol and flight characteristics. The one or more control surfaces mayinclude one or more air foils, winglets, elevators or ailerons. Forexample and as shown in FIGS. 1A-1G, winglets 134 mounted on the forwardsection or module 126 of the fuselage 104. Note that the one or moreairfoils or winglets can be retractable, removable, stowable or variableswept.

As shown, the closed wing 102, fuselage 104 and spokes 106 are notsubstantially reconfigured for transition between vertical takeoff andlanding, stationary flight and forward flight. However, in someembodiments it may be desirable to have the one or more spokes 106operable to change a position of the closed wing 102 with respect to thefuselage 104 or vice versa. In other words, the spokes 106 wouldselectively pivot the closed wing 102 to act like a giant flap inhorizontal mode and/or assist in transition to/from vertical mode.

The aircraft 100 provides a stable platform for one or more sensors orsurveillance packages disposed on, disposed within or attached to theclosed wing 102, spokes 106 or fuselage 104. In fact, the configurationof the aircraft 100 allows the placement of the one or more sensors orsurveillance packages to provide a 360 degree view. Moreover, theextension of the fuselage 104 from the engines or motors 132 provides awide unobstructed view for the one or more sensors or surveillancepackages.

As shown in FIG. 6C and FIGS. 7A-7G, the propellers 120 can beselectively folded in a forward direction. The propellers 120 could alsobe folded in a backward direction. In the embodiment having the forwardfolding propellers 700, each propeller 700 includes two or more rotorblades 702, each rotor blade 702 in mechanical communication with a hub704 and pivotable about an axis of rotation 118. A fold linkagemechanically couples a rotating portion of a bearing plate to the rotorblade 702. An actuator is coupled to a non-rotating portion of thebearing plate and is operable to reposition the bearing plate from afirst position to a second position such that the folding links pivotthe rotor blades 702 from a deployed position to a folded position. Thefolded position can be a forward direction, which extends past the hub704 with the first position of the bearing plate is closer to the hub704 than the second position of the bearing plate. A tip of all therotors 702 can be preloaded together in the forward folded position suchthat a vibration of the rotors 702 is minimized.

Alternatively and as shown in FIG. 8, the folded position can be abackward direction, which extends away from the hub 704, and the firstposition of the bearing plate is closer to the hub 304 than the secondposition of the bearing plate. The angle or distance that the rotors 702can fold will depend on the relative size and shape of the closed wingwith respect to the pivot point and size of the rotors. For example,FIG. 8 shows the rotors 702 folded in a backward position, but notagainst the surface of the closed wing 102 or substantially parallel tothe rotational axis 118 of the rotors 702. Some embodiments of thepresent invention will have the rotors 702 resting against or close tothe surface of the closed wing 102 and/or substantially parallel to therotational axis 118 of the rotors. An example of backward folding rotorblades is disclosed in U.S. Pat. No. 9,156,545 which is herebyincorporated by reference in its entirety.

Now referring to FIGS. 9A-9G, various views of a closed wing aircraft900 having a sinusoidal-shaped circular wing in accordance with oneembodiment of the present invention are shown. More specifically, FIG.9A is a perspective view, FIG. 9B is a front elevation view, FIG. 9C isa rear elevation view, FIG. 9D is right side elevation view, FIG. 9E isa left side elevation view, FIG. 9F is a top plan view, and FIG. 9G is abottom plan view. As shown, the leading edge 902 and trailing edge 904of the closed wing 906 are sinusoidal-shaped. Instead of the circularwing being a constant height around the center fuselage 104 aspreviously shown, the wing rises and falls to create three sinusoidalhumps 908 a, 908 b, 908 c. The humps 908 a, 908 b, 908 c are at theirhighest between the three spokes 106 and lowest where the wing 906attaches to the spokes 106. The advantages of this configuration are asfollows: 1) Additional wing ground clearance to the circular wing whenlanding. With the flat circular wing landing must be close toperpendicular to avoid damaging the wing or the landing gear must bemade much longer. 2) Improved access to center fuselage. With the flatcircular wing access to the center fuselage is restricted by the heightof the wing. 3) Improved stability by moving the wing center of pressurecloser to the aircrafts center of gravity. The same benefits areachieved but to a lesser degree with four sinusoidal humps and fourspokes and two sinusoidal humps with two spokes. With more than foursinusoidal humps the benefits are negligible. Alternatively, only one ofthe leading edge 902 or the trailing edge 904 of the closed wing 906 issinusoidal-shaped. Moreover, other wing shapes can be used.

It will be understood that particular embodiments described herein areshown by way of illustration and not as limitations of the invention.The principal features of this invention can be employed in variousembodiments without departing from the scope of the invention. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, numerous equivalents to the specificprocedures described herein. Such equivalents are considered to bewithin the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specificationare indicative of the level of skill of those skilled in the art towhich this invention pertains. All publications and patent applicationsare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.” Throughout this application, the term “about” is used toindicate that a value includes the inherent variation of error for thedevice, the method being employed to determine the value, or thevariation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps. In embodiments of any of the compositions andmethods provided herein, “comprising” may be replaced with “consistingessentially of” or “consisting of”. As used herein, the phrase“consisting essentially of” requires the specified integer(s) or stepsas well as those that do not materially affect the character or functionof the claimed invention. As used herein, the term “consisting” is usedto indicate the presence of the recited integer (e.g., a feature, anelement, a characteristic, a property, a method/process step or alimitation) or group of integers (e.g., feature(s), element(s),characteristic(s), propertie(s), method/process steps or limitation(s))only.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation,“about”, “substantial” or “substantially” refers to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skilled in the art recognizethe modified feature as still having the required characteristics andcapabilities of the unmodified feature. In general, but subject to thepreceding discussion, a numerical value herein that is modified by aword of approximation such as “about” may vary from the stated value byat least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15% from the stated value.

All of the methods disclosed and claimed herein can be made and executedwithout undue experimentation in light of the present disclosure. Whilethe methods of this invention have been described in terms of preferredembodiments, it will be apparent to those of skill in the art thatvariations may be applied to the methods and in the steps or in thesequence of steps of the method described herein without departing fromthe concept, spirit and scope of the invention. All such similarsubstitutes and modifications apparent to those skilled in the art aredeemed to be within the spirit, scope and concept of the invention asdefined by the appended claims.

What is claimed is:
 1. An aircraft capable of vertical takeoff andlanding and stationary flight, comprising: a closed wing; a fuselage atleast partially disposed within a perimeter of the closed wing; one ormore spokes coupling the closed wing to the fuselage; a plurality ofhydraulic or electric motors disposed within or attached to the closedwing, fuselage or spokes in a distributed configuration; a propellerproximate to a leading edge of the closed wing or the one or morespokes, operably connected to each of the hydraulic or electric motorsand that provide lift whenever the aircraft is in vertical takeoff andlanding and stationary flight; a source of hydraulic or electric powerdisposed within or attached to the closed wing, fuselage or spokes andcoupled to each of the of hydraulic or electric motors disposed withinor attached to the closed wing, fuselage or spokes, wherein the sourceof hydraulic or electric power provides sufficient energy density forthe aircraft to attain and maintain operations of the aircraft; acontroller coupled to each of the hydraulic or electric motors; and oneor more processors communicably coupled to each controller that controlan operation and speed of the plurality of hydraulic or electric motors.2. The aircraft of claim 1, wherein the hydraulic or electric motors areselected based on at least one of aerodynamics, propulsive efficiency,structural efficiency, aeroelasticity, or weight of the aircraft.
 3. Theaircraft of claim 1, wherein the aircraft is manned or unmanned.
 4. Theaircraft of claim 1, wherein the source of hydraulic or electric poweris one or more batteries, a piston engine, or a turboshaft engine. 5.The aircraft of claim 1, wherein the plurality of hydraulic or electricmotors comprise 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, or 25 hydraulic or electric motors.
 6. Theaircraft of claim 1, wherein the propeller is at least one of a variablepitch, a constant pitch, a rear folding, or a forward folding propeller.7. The aircraft of claim 1, wherein the hydraulic motors are definedfurther as a variable displacement hydraulic engine, wherein a speed anda torque are controlled by changing a displacement of the variabledisplacement hydraulic engine.
 8. The aircraft of claim 1, wherein thehydraulic or electric motors are self-cooling.
 9. The aircraft of claim1, wherein the source of hydraulic or electric power comprises aturboshaft engine or an internal combustion engine, and a variabledisplacement hydraulic pump connected between the turboshaft engine orthe internal combustion engine and the plurality of hydraulic orelectric motors.
 10. The aircraft of claim 1, wherein the source ofhydraulic or electric power comprises one or more batteries, and avariable displacement hydraulic motor pump or a piezo-hydraulic pumpconnected between the one or more batteries and the plurality ofhydraulic or electric motors.
 11. A method for distributed propulsion ofaircraft capable of vertical takeoff and landing and stationary flightcomprising: determining at least one of aerodynamics, propulsiveefficiency, structural efficiency, and weight of the aircraft; selectinga number, size and type of hydraulic or electric motors necessary toprovide distributed propulsion for powered operations of the aircraft;selecting a power source having sufficient energy density to power thehydraulic or electric motors connected to propellers to operate theaircraft; and providing a distributed propulsion system comprising: aclosed wing; a fuselage at least partially disposed within a perimeterof the closed wing; one or more spokes coupling the closed wing to thefuselage; a plurality of hydraulic or electric motors disposed within orattached to the closed wing, fuselage or spokes in a distributedconfiguration; a propeller proximate to a leading edge of the closedwing or the one or more spokes, operably connected to each of thehydraulic or electric motors and that provide lift whenever the aircraftis in vertical takeoff and landing and stationary flight; a source ofhydraulic or electric power disposed within or attached to the closedwing, fuselage or spokes and coupled to each of the of hydraulic orelectric motors disposed within or attached to the closed wing, fuselageor spokes, wherein the source of hydraulic or electric power providessufficient energy density for the aircraft to attain and maintainoperations of the aircraft; and a controller coupled to each of thehydraulic or electric motors; and one or more processors communicablycoupled to each controller that control an operation and speed of theplurality of hydraulic or electric motors.
 12. The method of claim 12,further comprising calculating aerodynamics, propulsive efficiency,structural efficiency, or aeroelasticity, and selecting the number,power output, and type of hydraulic or electric motors used fordistributed propulsion.
 13. The method of claim 12, wherein the sourceof hydraulic or electric power is one or more batteries, a pistonengine, or a turboshaft engine.
 14. The method of claim 12, wherein theplurality of hydraulic or electric motors comprise 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25hydraulic or electric motors.
 15. The method of claim 12, wherein thepropeller is at least one of a variable pitch, a constant pitch, a rearfolding, or a forward folding propeller.
 16. The method of claim 12,wherein the hydraulic motors are defined further as a variabledisplacement hydraulic engine, wherein a speed and a torque arecontrolled by changing a displacement of the variable displacementhydraulic engine.
 17. The method of claim 12, wherein the hydraulic orelectric motors are self-cooling.
 18. The method of claim 12, whereinthe source of hydraulic or electric power comprises a turboshaft engineor an internal combustion engine, and a variable displacement hydraulicpump connected between the turboshaft engine or the internal combustionengine and the plurality of hydraulic or electric motors.
 19. The methodof claim 12, wherein the source of hydraulic or electric power comprisesone or more batteries, and a variable displacement hydraulic motor pumpor a piezo-hydraulic pump connected between the one or more batteriesand the plurality of hydraulic or electric motors.